Implantable conducting lead

ABSTRACT

An electrically conducting lead ( 20 ) that can used in the body for electrical stimulations applications, such as a cochlear implant. The lead comprises a body of relatively electrically insulative material ( 41 ) having a relatively electrically conductive element ( 18 ) extending therethrough in a wound arrangement. The electrically conductive element ( 18 ) is comprised of a plurality of layers of electrical conductors ( 14 ). The conductive element ( 18 ) is disposed in the lead such that the longitudinal extent of each of the electrical conductors ( 14 ) is the same.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of and is a national stageapplication of PCT Application No. PCT/AU2003/001369, entitled,“Implantable Conducting Lead,” filed on Oct. 16, 2003, which claims thepriority of Australian Patent No. 2002952146, filed on Oct. 17, 2002.The entire disclosure and contents of the above applications are herebyincorporated by reference.

TECHNICAL FIELD

The present invention relates to an electrically conducting leadsuitable for use with an implantable medical device. More particularly,the present invention relates to an implantable conducting lead having alayered conducting element with multiple conducting portions.

BACKGROUND OF THE INVENTION

Medical devices capable of being implanted in the body to providetherapy to a recipient have become increasingly common over recenttimes. Devices such as pacemakers, defibrillators, cochlear implants andfunctional electrical stimulation systems have all proven successful inproviding useful therapy to recipients across a broad spectrum ofapplications.

Fundamental to all such devices is the provision of an implantablestimulator unit fixedly implanted within the body of the recipient. Thisstimulator unit is typically capable of receiving control signals from adevice external to the recipient via a transcutaneous link. As well ascontrol signals, the implanted stimulator unit may also receive powerfrom an external device via the same or an alternative transcutaneouslink.

Upon receipt of control signals and/or power, the stimulator unittypically then directs and controls the stimulation to be applied by thesystem. In the case of cochlear implants, the stimulator system mayselect the desired electrode and send a stimulation pulse to theelectrode having a desired amplitude and pulse width. Typically, thestimulator unit is provided with dedicated electronics which enable itto decode the received control signals and control the flow ofstimulation current from the stimulator unit to the desired stimulationsite.

With advancement in battery technology, it is becoming increasinglypopular for implanted stimulator units to be provided with their ownpower source, usually in the form of a rechargeable battery, to provideoperating power to the electronics of the stimulator unit. In thisregard, such devices can operate, at least for a period of time withoutthe need for any external devices. This is important for pacemakerdevices as they do not need to rely upon a constant link with anexternal device to remain operational, and can continue to perform theirimportant function by relying on their own power source. For devicessuch as cochlear implants, there is an increasing desire for suchdevices to operate invisibly without the need for external devices andfor this reason the use of an implantable stimulator unit with its ownpower source is becoming increasingly desirable.

Apart from the implanted stimulator unit which houses the electroniccircuitry and power source necessary to control the therapy applied bythe implantable device, a means for actually applying the therapy isalso fundamental to such systems. In most cases, the means for applyingthe therapy is typically one or more electrodes, strategicallypositioned close to the desired stimulation site, for applying theelectrical stimulation to that particular site.

The stimulating electrodes are typically positioned remote from theimplanted stimulator unit. For example, in cochlear implant applicationsthe stimulator unit is typically positioned in a recess in the skullwhilst the electrodes are implanted in the cochlea close to the desirednerves. In this regard, a lead connecting the electrodes and thestimulator unit is required, and such leads need to be designed in amanner to ensure that the electrical stimulation is delivered safely tothe appropriate electrodes and that the link between the stimulatingelectrodes and the stimulator unit is sturdy and reliable.

Traditionally, the common way of providing this electrical connectionbetween the stimulator unit and the electrodes has been via conductingwires within the lead. Such wires typically communicate with theelectronics within the stimulator unit via a hermetic feedthrough deviceand are welded to the terminating electrodes thereby forming aconductive path from the stimulator unit to the electrodes along whichthe stimulation current can flow. Typically, the lead is insulated fromthe surrounding tissue via a coating of insulative material, such assilicone.

In providing such an implantable connecting lead, it is important thatthe lead is capable of a degree of flexibility to compensate for anymovement between the implantable stimulator and the electrodes, such asmovement which may naturally occur due to body growth. Without suchflexibility, excessive force can be experienced in the lead,particularly at the connection points such as at the feedthrough,resulting in the lead failing to act as a conductor. Further to this,providing a flexible rather than a rigid connection between theelectrodes and the stimulator unit provides for easier surgicalplacement of the electrodes close to the desired stimulation site, whichensures that the surgical procedure is simpler and requires lesssurgical skill.

The typical method of providing a lead capable of a degree offlexibility is to dispose the wires, either individually or as a group,in a helical arrangement along the length of the lead. The wires canthen be enclosed in a coating of body-compatible polyurethane, or asuitable nonconductive plastic which has a requisite degree offlexibility. In this way, the lead can experience a degree of elongationwithout placing undue stress on the wires or at the point where thewires connect to the stimulator unit. Examples of such leads aredescribed in U.S. Pat. No. 4,835,853 and International PatentApplication Publication No WO 83/04182.

One problem with such prior art methods is that it is difficult to sortthe wires in a manner that makes it easily identifiable which electrodethey are connected to. As such, following the formation of the lead, itis a time consuming process to individually test each wire and identifywhich electrode it is connected to and to then ensure that this wire isconnected to the stimulator unit in the appropriate manner. This problemis further exacerbated when the number of stimulating electrodesincreases and hence the number of wires increases, such as in cochlearimplants where the number of electrodes can be greater than 22.

The present applicant has developed a new process for manufacturingelectrodes and conductors that connect the electrodes to astimulator/control unit. This process and the resulting products aredescribed in detail in International Patent Application No.PCT/AU02/00575, the contents of which are incorporated herein byreference. In essence, this process results in the formation of anelectrode array comprising of a stack of offset electrodes, layered ontop of each other. Each of the electrodes has a respective conductingportion extending from the electrode, with the conducting portion andthe electrode being integral and constructed from one piece of material.In this regard, a connecting lead is provided consisting of a pluralityof layered, parallel conducting portions extending in a longitudinaldirection. Such a lead therefore resembles a layered ribbon conductor,considerably different from conventional wire leads.

With such a change in the traditional structure of conventional wireconductors used in implantable devices, there is a need to provide aconducting lead that is capable of maintaining the conductors in aflexible and insulative environment. Further to this, there is a need toprovide a conducting lead that can take advantage of the orderedstructure of layered conducting wires so that the conductors can beeasily sorted and connected to the appropriate stimulator.

Any discussion of documents, acts, materials, devices, articles or thelike which has been included in the present specification is solely forthe purpose of providing a context for the present invention. It is notto be taken as an admission that any or all of these matters form partof the prior art base or were common general knowledge in the fieldrelevant to the present invention as it existed before the priority dateof each claim of this application.

SUMMARY OF THE INVENTION

Throughout this specification the word “comprise”, or variations such as“comprises” or “comprising”, will be understood to imply the inclusionof a stated element, integer or step, or group of elements, integers orsteps, but not the exclusion of any other element, integer or step, orgroup of elements, integers or steps.

According to a first aspect, the present invention is an electricallyconducting lead comprising:

a body of relatively electrically insulative material; and

a relatively electrically conductive element extending through at leasta portion of said insulative body in a helically wound arrangement;

wherein said electrically conductive element comprises a plurality oflayers of electrical conductors, with each layer of electricalconductors being made up of a plurality of separate electricalconductors, with the position of each electrical conductor beingconstant with regard to its neighbour and the position of each layer ofelectrical conductors being constant with regard to its neighbouringlayer over the length of said portion of said insulative body.

In a further embodiment of this aspect, the electrically conductiveelement extends from a first end to a second end of the lead.

According to a second aspect, the present invention is an electricallyconducting lead comprising:

a body of relatively electrically insulative material; and

a relatively electrically conductive element extending through at leasta portion of said insulative body in a wound arrangement;

wherein said electrically conductive element comprises a plurality oflayers of electrical conductors with the longitudinal extent of each ofsaid electrical conductor over said portion of the lead beingsubstantially identical.

In this aspect, the wound arrangement of the electrically conductiveelement is preferably a helically wound arrangement. In this regard, thespacing or pitch of the wound arrangement can vary or be identical alongsaid arrangement.

In a further embodiment of this aspect, the electrically conductiveelement extends from a first end to a second end of the lead. In thisembodiment, the longitudinal extent of each of said electricalconductors over the length of the lead from the first end to the secondend is substantially identical. More preferably, the longitudinal extentof the electrical conductors is identical.

In one embodiment, the electrically conductive element extending throughsaid portion of the insulative body is wound in an anticlockwisedirection and then in a clockwise direction if looking at the lead fromthe first end of the lead. It will be understood that if one was to lookat the lead from the second end, the anticlockwise turns would appear tobe turning clockwise and the clockwise turns anticlockwise. Stillfurther, it will be appreciated that the electrically conductive elementcould be wound in a clockwise direction away from the first end and thenin an anticlockwise direction, if looking at the lead from its firstend.

In a preferred embodiment, the length of the conductive element that iswound in an anticlockwise manner is substantially equal, and preferablyis equal, to the length of the conductive element that is wound in aclockwise manner.

At the transition from anticlockwise to clockwise turns, the conductiveelement is preferably folded back on itself.

In another embodiment, the conductive element continues to be wound inan anticlockwise manner or clockwise manner, when viewed from the firstend, for the length of said portion of the insulative body. In thisembodiment, the layer is preferably twisted by 180° at a location alongthe length of the body. In a preferred embodiment, the twist is atabout, and preferably exactly at, the midway point of the length of thewound conductive element in the lead.

Each layer of the conductive element is preferably comprised of aplurality of separate electrical conductors. Each layer can have thesame number of conductors as the other layers in the element. In anotherembodiment, the number of conductors of at least one of the layers canvary from the number in one, more or all of the other layers of theelement.

According to a third aspect, the present invention is an electricallyconducting lead comprising:

a body of relatively electrically insulative material; and

a relatively electrically conductive element extending through at leasta portion of said insulative body in a wound arrangement;

wherein said electrically conductive element comprises a plurality oflayers of electrical conductors with the number of conductors of atleast one of the layers varying from the number of conductors in atleast one of the other layers of the element.

In this aspect, the number of conductors in said one of the layersvaries from the number in more than one, or all, of the other layers ofthe element.

In a further embodiment of this aspect, the electrically conductiveelement extends from a first end to a second end of the lead. In thisembodiment, the longitudinal extent of each of said electricalconductors over the length of the lead from the first end to the secondend is substantially identical. More preferably, the longitudinal extentof the electrical conductors is identical.

In this aspect, the wound arrangement of the electrically conductiveelement is preferably a helically wound arrangement. In this regard, thespacing or pitch of the wound arrangement can vary or be identical alongsaid arrangement.

In each of the aspects, the electrical conductors are preferably made ofplatinum. More preferably, the electrical conductors are made from asheet of platinum. Each of the leads preferably has a first end that isattachable to or is integrally attached to an electrode pad. Each of theleads further preferably has a second end that is connectable to astimulator unit that delivers electrical signals through the lead.

In one embodiment of each of the aspects, the lead is preferablyimplantable in the body of a recipient. In this regard, the materialsused to form the lead are preferably suitable for implantation in thebody of a recipient.

The electrically insulative body is further preferably formed from aflexible material. Examples of suitable materials include siliconerubber and parylene.

According to a fourth aspect, the present invention is a method ofmanufacturing a lead according to any one of the preceding aspects, themethod comprising the step of:

winding a conductive element relative to and around an insulative body.

In one embodiment, the conductive element can be loaded in a spindle,with one end of the element attached to one end of the insulative body.The insulative body can then be turned in one direction, such as aclockwise direction, causing the conductive element to exit the spindleand become wound around the insulative body. The spindle can be movedlongitudinally relative the length of the insulative body.

In one embodiment, the spindle could move in a clockwise directionrelatively around the insulative body. If desired, at a mid point alongthe length of the insulative body, the direction of rotation of theinsulative body with respect to the spindle can change to ananticlockwise direction. At this point, the conductive element is causedto fold upon itself such that what was an inner layer of the conductiveelement becomes the outer layer and vice versa. The conductive elementis then wound onto the insulative body in an opposite direction for alength equal to that previously wound onto the insulative body. Thisresults in all layers of the conductive element travelling the samedistance and therefore being aligned at both ends of the lead.

Following winding of the conductive element, the insulative body can becoated in another layer of insulative material, such as silicone.

In an alternative method, respective ends of the conductive element canbe fixed to respective ends of the insulative body, with the spindlepositioned midway between both ends of the insulative body. Once again,the insulative body can be rotated relative to the spindle or thespindle can rotate relative to the insulative body to cause theconductive element to be wound onto the insulative body. As theconductive element is wound onto the insulative body, the spindle movesrelatively closer to the insulative body to ensure that the pitch ofwinding is controlled as desired.

At the mid-point, the winding is complete and the conductive element isremoved from the spindle, with all layers of the conducting elementtravelling the same distance over the length of the insulative body.

In a still further embodiment, the conductive element is again mountedin a spindle with one end of the conductive element connected to one endof the insulative body. When the spindle has wound the conductiveelement to the mid-point, the spindle is preferably relatively rotatedabout or exactly 180°. This causes the conductive element to twist suchthat what was previously the inner layer of the conductive elementbecomes the outer layer and what was previously the outer layer becomesthe inner layer of the conductive element.

Following the formation of the twist in the conductive element, theinsulative body is preferably continued to relatively rotate in the samedirection to complete the winding.

Use of the methods as defined herein result in the formation of a leadcomprising an insulative body having a conductive element wound therein,with preferably, the conductors of the element extending the same lengththrough the lead.

According to a fifth aspect, the present application comprises anelectrically conducting lead comprising at least one wire set, each setcomprising at least two electrically insulated wires extending acrossthe set in a first direction and disposed substantially in aside-by-side relationship, wherein the set has an undulating form for atleast a portion of its length defined by a plurality of ridges andtroughs extending across the set in a direction that is at an angle tosaid first direction.

According to a sixth aspect, the present application comprises atissue-stimulating prosthesis comprising at least one stimulator meansthat outputs electrical signals via an electrically conducting lead toan electrode array, the lead comprising at least one wire set connectingthe stimulator means to the electrodes of the array, each set comprisingat least two electrically insulated wires extending across the set in afirst direction and disposed substantially in a side-by-siderelationship, wherein the stack has an undulating form for at least aportion of its length defined by a plurality of ridges and troughsextending across the set at an angle to said first direction.

In a preferred embodiment of the fifth and sixth aspects, the ridges andundulations are parallel. Still further, the ridges and undulations arepreferably substantially at right angles to said first direction. Thepeak to peak amplitude of pairs of ridges and troughs is preferably atleast substantially constant across the lead. It will, however, beappreciated that the peak to peak amplitude could vary along the lengthof the lead.

In a further embodiment of the fifth and sixth aspects, the undulatingform of the lead is at least substantially sinusoidal. Other waveformscan, however, be envisaged. Still further, the undulating form of thelead extends at least a majority of the length of the lead. In a furtherembodiment, the undulating form extends the entire length of the lead.In yet a further embodiment, the undulating form extends in separatesections along the lead with each section separated by a length ofstraight lead.

In a preferred embodiment, each wire comprises a longitudinal portion ofa conductive material such as platinum, iridium, or gold encapsulatedwithin a layer of silicone and/or parylene. The conductive material canhave a thickness of between about 10 and 50 microns. In each set, thewires are preferably formed in a planar side by side relationship. Stillfurther, the respective wires are substantially parallel.

Each wire preferably extends from a respective single electrode of anelectrode array. The electrode array can be formed from a stack of aplurality of sets of electrodes. In one embodiment, the array cancomprise 30 electrodes, with the array made up of 5 different sets ofelectrodes that have been formed individually and then stacked one ontop of the other to form a single electrode array. Where the arraycomprises 30 electrodes, the array can comprise 3 sets of sevenelectrodes, 1 set of 5 electrodes and 1 set of 4 adjustable electrodes.In this embodiment, the 3 sets of 7 electrodes are stacked one on top ofthe other, the set of 5 electrodes is stacked on these sets, with theset of 4 electrodes on top of the stack. Other combinations of sets can,however, be envisaged.

While the sets of electrodes are stacked one upon the other, it will beappreciated that the actual position of the electrodes in each set arenot necessarily vertically aligned. Rather, the set immediately aboveits lower set may be laterally offset so as to ensure the electrodes arevisible from beneath the stack. The stacks could also be verticallyaligned.

In a further embodiment, the electrodes and wires can be formed usingelectrical discharge machining (EDM), milling, etching or laser cutting.

The wires extending from each electrode are preferably of the samelength. It can, however, be envisaged that the wires could be formedwith different lengths to account for the ultimate offset present whenforming the stack.

In a further embodiment of the fifth and sixth aspects, the lead canfurther comprise an outer layer encapsulating at least said portion ofthe lead that has the undulating form. The outer layer can besubstantially rectangular in cross-section. In another embodiment, theouter layer can be tubular with said undulating portion disposed in alumen of the tube.

In a further embodiment, the undulation in the lead is formed by passingthe lead between at least two wheel or rollers having interengagingteeth. The shape, size and spacing of the teeth is adapted to result inthe desired undulating form in the lead. It will be appreciated that theundulating form can be changed by making appropriate changes to thewheels or rollers or using alternative wheels or rollers as required.

The presence of the undulating form in the lead improves the flexibilityof the lead and allows it to compensate for any movement between thestimulating means and the electrode array. This serves to minimise forceon feedthroughs used to connect the wires to the stimulator means.

In a preferred embodiment, the tissue-stimulating prosthesis cancomprise a cochlear implant system.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example only, preferred embodiments of the invention are nowdescribed with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a prior art lead used in implantabledevices;

FIG. 2 is a view of electrode pads and conducting portions according toone embodiment of the present invention;

FIG. 3 is a top view of an electrode array arrangement;

FIG. 4 is a cross sectional view of the conductive element of FIG. 3along X-X;

FIG. 5 is a side view of the conductive element of FIG. 4;

FIG. 6 is a view of one embodiment of the conductive lead according tothe present invention;

FIGS. 7 a and 7 b are end views of the conductive element of FIG. 6;

FIG. 8 is a side view of one end of the conductive element of FIG. 7 a;and

FIG. 9 is a view of another embodiment of the conductive lead of thepresent invention;

FIG. 10 is a view of yet another embodiment of the conductive lead ofthe present invention;

FIGS. 11 a-11 c depict the steps associated with one method ofconstructing the conductive lead as shown in FIG. 9;

FIGS. 12 a-12 c depict the steps associated with another method ofconstructing the conductive lead as shown in FIG. 9;

FIGS. 13 a-13 c depict the steps associated with a still further methodembodiment of constructing the conductive lead as shown in FIG. 10;

FIG. 14 depicts a pair of gear wheels for forming an undulation in atleast a portion of the lead;

FIGS. 15 a-15 c depict an undulating lead formed using the gear wheelsof FIG. 14; and

FIGS. 16 a-16 b are photos depicting another embodiment of an undulatinglead according to the present invention.

PREFERRED MODE FOR CARRYING OUT THE INVENTION

FIG. 1 depicts generally as 10 one example of a conventional conductinglead that is used in implantable medical devices. This lead 10 has aplurality of conducting wires 2 extending therethrough. Each of thesewires 2 can be connected at one end to a stimulator unit and at theother end to a stimulating/sensing electrode so that an electric signalcan be transmitted from the stimulator unit to the correspondingelectrode. The wires 2 are typically embedded in a body-compatiblematerial 4, such as polyurethane, an organo-silicon polymer, or anyother suitable non-conductive plastic.

Typically, the body-compatible material 4 can undergo some degree ofextension or flex. As shown, each of the wires 2 are arranged within thebody compatible material 4 in a helical manner to ensure that the lead10 can extend without placing undue stress on the wires 2. As is shown,the pitch of the wire helix can also be altered to vary the flexibilityof the conducting lead 10 along its length.

FIGS. 2 and 3 depict one arrangement of stimulating electrode pads andleads for use in the present invention. This particular arrangement isdescribed in more detail in International Patent Application No.PCT/AU02/00575, the contents of which is incorporated herein byreference. In this application, the present invention is described inrelation to a cochlear implant application, however it will beappreciated that the present invention is also applicable to otherapplications that employ a conducting lead to deliver electrical signalsor pulses.

FIG. 2 depicts the electrode pads 12 and conducting portions 14 (i.e.the electrically conducting leads for each electrode pad 12) as beingformed in a series of groups that are herein labelled as groups A-F. Asis clearly evident, the electrode pads 12 and the conducting portions orwires 14 are formed as one piece. In the depicted embodiment, they areformed from a sheet of suitable conductive material, such as platinum,in accordance with the methods described in Application No.PCT/AU02/00575. The electrode pads 12 and wires 14 are made from a sheetof platinum or similar conducting material, and covered in a coating ofelectrically insulating material such as silicone rubber or a polymermaterial such as parylene.

The electrode pads 12 are then shaped accordingly to suit theapplication. In the depicted embodiment, the pads 12 are shaped into aU-shape, with the wires 14 running centrally from the electrode pads 12(see FIG. 3). In this example, each of the electrode array groups A-Fare formed separately, but preferably from a single sheet of platinum,thereby forming a series of electrode arrays, with each array consistingof a plurality of electrode pads 12 with centrally positioned wires 14connected thereto.

Each of the electrode array groups A-F can be arranged longitudinally,to form a multi-electrode array structure 15. Such an array can then beused, for example, as a cochlear implant electrode array. In theembodiment shown, electrode array group A is stacked and positioned ontop of electrode array group B which is then stacked and positioned ontop of electrode array group C, and so on. This arrangement produces anelectrode array structure that is shown more clearly from the top viewof the structure provided as FIG. 3.

In the embodiment shown in FIG. 3, the electrode array structure 15consists of 30 individual electrode pads 12, with each electrode pad 12having an integral conducting portion or wire 14 extending therefrom andrunning centrally along the electrode array structure 15. Following theformation of the electrode array structure 15, the array can be mouldedin a suitable bio-compatible material 41 such as silicone and shapedaccordingly, as is known in the art and which is not essential to anunderstanding of the present invention.

In the embodiment described, the electrode array structure is shownconsisting of 30 individual electrode pads 12, however it should beappreciated that the electrode array structure could consist of anynumber of electrode pads and still be applicable to the presentinvention.

In an electrode array constructed in the manner shown in FIGS. 2 and 3,the conducting portions 14 resulting from such an arrangement will beformed in the manner shown in FIG. 4. In this regard, FIG. 4 can beconsidered a cross-section of the conducting portions 14 of FIG. 3 alongline X-X. As is clearly evident, the conducting portions 14 associatedwith each of the electrode array groups A-F are arranged in a layeredformat, with the most distant electrode array group A being the toplayer, and the most proximal electrode array group F being the bottomlayer, this layered format being generally referred to as the conductingelement 18.

This conducting element 18 is more clearly shown in FIG. 5, which is aside view of the conducting element 18 shown in FIG. 4. From thesefigures, it is evident that the resulting format of the conductingelement 18 has a layered, ribbon-like format with each of the conductingportions 14 connected to an integral electrode pad 12 at one end andconnectable to a stimulator unit at the other end via a suitablefeedthrough device. It is also to be understood in looking at FIG. 4that each of the conducting portions 14 are electrically insulated fromall of the other conducting portions in the element 18.

In the embodiment shown in FIG. 4, the conducting element 18 is made upof six layers (A-F) however the number of layers is dependant upon thedesign of the electrodes and as such any number of layers could be usedas desired. Also, FIG. 4 depicts the conducting element 18 being made upof layers having different numbers of conducting portions 14, forexample layer A is depicted as having 3 conducting portions, layer Bwith 4, layer C with 5 and layers D-F with 6 conducting portions. Itshould be appreciated that the number of conducting portions 14 providedin each of the layers is not critical to the present invention as thelayers could all contain the same number of conducting portions or allcontain different numbers and still fall within the scope of the presentinvention.

In the embodiment shown in FIG. 4, each of the conducting portions 14are shown having a substantially square cross-sectional area. It shouldbe appreciated however that the conducting portions could be of anycross sectional shape. The dimensions of the conducting portions 14shown also vary dependant upon the desired application. Possibledimensions of the conducting portions may have a width Y of betweenabout 5-50 μm and a thickness Z of between about 10-100 μm. In thedepicted embodiment, the width Y of the conducing portions is 25 μm andthe thickness Z is 15 μm.

As the conducting portions 14 together form a layered, ribbon-likeconducting element 18, each of the portions 14 cannot easily beseparated and individually coiled to form a helical conducting lead asis typical in the prior art and shown in FIG. 1. Instead, it isdesirable to form a connecting lead wherein the conducting element 18 ismaintained in a layered, ribbon format within a coating of insulativeand biocompatible material, such as a silicone or parylene.

Therefore the formation of such a lead that is capable of providingadequate flexibility and elongation as well as being bio-compatible andinsulative is important in providing a safe and effective connectionbetween an implantable stimulator unit and stimulating electrodes.

FIG. 6 depicts one embodiment of a conducting lead according to thepresent invention. In this embodiment, the lead 20 includes a conductingelement 18 helically wound within a body of insulative material havinggood body compatibility, such as a silicone or parylene. As is depicted,the conducting element 18, which is shown in cross-section detail inFIGS. 7 a and 7 b, is made up of a plurality of layers with each layerconsisting of a plurality of conducting portions 14. The pitch of thehelix is controlled so that the flexibility of the lead 20 can bealtered as desired. One end of the lead 20 is preferably connected to astimulator unit, whilst the other end of the lead may be connected tostimulating electrodes, such as those shown in FIGS. 2 and 3.

FIGS. 7 a and 7 b show cross-sectional views of the conducting element18 at each end of the lead 20. As shown in FIG. 7 a, the conductingelement 18 may consist of a plurality of layers of conducting portions14 with each layer having the same number of conducting portions 14. Itwill be appreciated that the conducting element may be as is depicted inFIG. 4, with some of the layers having different numbers of conductingportions 14.

In this embodiment, by providing a layered conducting element 18 theposition of the conducting portions 14 with respect to each other can bemaintained throughout the length of the lead 20. As is shown in FIGS. 7a and 7 b, conducting portion A1 can be easily identifiable at both endsof the lead 20 allowing for easy determination and connection of theelectrode to the appropriate contact. In prior art devices wherebyindividual or bunched wires are helically wound within an insulativematerial (as depicted in FIG. 1), such direct identification is noteasily provided for. Providing such easy identification of theconducting portions 14 allows for considerable time reductions in themanufacture of such devices. Without this, the task of connecting thelead to the stimulator is particularly arduous, as each connectingportion must be individually tested to determine the electrode pad 12 towhich it is connected. This time saving aspect becomes particularlyimportant when the number of electrode pads 12 is increased, requiringmuch sorting of the conducting portions 14 prior to connection to thestimulator unit.

In the embodiment depicted in FIG. 6, each of the layers of theconducting element 18 are not aligned at both ends. The result of thisis depicted in FIG. 8, which shows one end of the conducting element 18of the present invention. This difference in alignment is because theouter layer (A) of the conducting element 18 will travel a greaterdistance in the helix than the inner layer (F) of the conducting element18. In some instances, the alignment of each of the conducting portions14 at both ends will not be critical, as the conducting portions may beseparately connected to the stimulator unit using an appropriatefeedthrough device.

FIGS. 9 and 10 depict embodiments of the present invention similar tothe embodiment shown in FIG. 6, but which provide for alignment of theconducting portions 14 at both ends of the lead 20.

In the embodiment shown in FIG. 9, the conducting element 18 ishelically wound in one direction, eg anti-clockwise, for a portion ofthe length of the lead 20, and then helically wound in an oppositedirection, eg clockwise, for another portion of the length of the lead20. In this regard, it is preferred that the conducting element 18 iswound such that each layer travels the same distance over the length ofthe lead, providing alignment of the conducting portions at both ends.This can be achieved by winding the conducting element 18 in onedirection for half the length of the lead 20 and at a midpoint 22,winding the conducting element 18 in the opposite direction for theremaining half of the lead. Alternatively, the conducting element 18 maybe wound in alternative directions for a number of cycles over thelength of the lead, ensuring that the cycles of both the clockwise andanticlockwise windings are identical over the length of the lead 20.

By controlling the point 22 at which the winding of the conductingelement 18 changes from clockwise to anti-clockwise, each layer ofconducting portions 14 of the conducting element 18 can be wound so thatthey each travel the same distance over the length of the lead 20. Inthe embodiment shown in FIG. 9, the point 22 where the winding changesdirection, is achieved by folding the conducting element back uponitself thereby causing the inside layer 31 i (the cross-hatched side) tobecome the outside layer 31 o and what was previously the outside layer32 o becomes the inside layer 32 i.

In the embodiment depicted in FIG. 10, an alternative method ofachieving this alignment is shown wherein the conducting element 18 istwisted by 180 degrees causing what was previously the inside layer 31 ito become the outside layer 31 o and what was previously the outsidelayer 32 o to become the inside layer 32 i. In this method, thedirection of winding does not have to be changed and by controlling thenumber of turns and the pitch of the winding, the distance travelled byeach layer of the conducting element 18 over the desired length of thelead 20 is controlled.

A lead 20, such as that shown in FIG. 9 can be manufactured in themanner depicted in FIGS. 11 a-11 c. In FIG. 11 a, a silicone tube 25 isshown placed over a mandrel 27 extending through the silicone tube 25and supported at both ends by chucks (not shown). A spindle 26 is thenloaded with the conducting element 18 for winding onto the silicone tube25. As shown in FIG. 11 a, the conducting element 18 is first fixed atone end of the silicone tube 25 prior to winding.

As shown in FIG. 11 b, the chucks supporting the mandrel 27 are thenturned in one direction, eg a clockwise direction, and the conductingelement 18 is caused to exit the spindle 26 and become wound around thesilicone tube 25. The spindle 26 can move longitudinally along thelength of the silicone tube 25 as it rotates. It will be appreciatedthat the tube 25 could also be moved longitudinally relative to astationary or moving spindle 26.

In one embodiment, the spindle 26 could move in a clockwise directionaround the silicone tube 25. At a mid point, shown in FIG. 11 b, thedirection of rotation of the silicone tube with respect to the spindle26 can change. At this point the conducting element 18 is then foldedupon itself, as described in relation to FIG. 9, such that the insidelayer becomes the outside layer and vice versa.

As shown in FIG. 11 c, the direction of rotation of the silicone tube 25then changes from clockwise to anti-clockwise, and the conductingelement 18 is then wound onto the silicone tube 25 in an oppositedirection. This results in all layers of the conducting element 18travelling the same distance and therefore being aligned at both ends ofthe lead. Following winding of the conducting element 18, the siliconetube 25 and mandrel 27 can be removed from the chucks and coated inanother layer of insulative material, such as silicone. The mandrel 27can then be removed from the silicone tube 25 and further insulativematerial such as silicone can then be injected into the space left bythe mandrel 27 to form a lead 20 as shown in FIG. 9.

An alternative method of manufacturing the lead of FIG. 9 is depicted inFIGS. 12 a-12 c. In this method the conducting element 18 is fixed atboth ends to the silicone tube 25, and the spindle 26 is positionedmidway between both ends of the silicone tube 25, as shown. Once again,the silicone tube 25 can be rotated relative to the spindle 26 or thespindle 26 can rotate relative to the silicone tube 25 to cause theconducting element 18 to be wound onto the silicone tube 25. As theconducting element 18 is wound onto the silicone tube 25, the spindlemoves relatively closer to the silicone tube 25 to ensure that the pitchof winding is controlled as desired.

At the mid-point, as shown in FIG. 12 c, the winding is complete and theconducting element 18 is removed from the spindle, with all layers ofthe conducting element travelling the same distance over the length ofthe silicone tube 25, producing a lead 20 as shown in FIG. 9.

A lead 20, such as that shown in FIG. 10 can be manufactured in themanner shown in FIGS. 13 a-13 c. In FIG. 13 a, the same arrangement asthat described in relation to FIG. 11 a is used. However, in thisembodiment, when the spindle 26 has wound the conducting element 18 tothe mid-point, as shown in FIG. 13 b, the spindle 26 is rotated 180degrees, as shown. In this regard, the conducting element 18 is“twisted” such that what was previously the inner layer of theconducting element 18 becomes the outer layer and what was previouslythe outer layer becomes the inner layer of the conducting element 18.This is shown in more detail in FIG. 10.

Following this “twist”, the silicone tube 25 and mandrel 27 arrangementis rotated in the same direction and the winding is completed. In thisregard, a lead similar to or the same as that shown in FIG. 10 iscreated with the winding occurring in one direction similar to thatshown in FIG. 6.

Whilst the above three embodiment describe a silicone tube 25 formingthe winding surface, it should be appreciated that other such materialscould be used to create such a lead. Other such materials could beparylene or any other material that is both insulative and flexible andwhich is also body-compatible.

Another lead arrangement is depicted in FIGS. 15 a to 16 b. Here, theplurality of stacked sets of conducting portions or wires 14 acttogether to form a lead 60 that is adapted to extend from a stimulator,such as the stimulator of a cochlear implant, to the electrodes 12. Oncethe lead 60 is formed, at least a portion of it distal from theelectrodes 12 can be passed through a set of toothed wheels 81,82 or thelike, such as is depicted in FIG. 14. The teeth of the wheels 81,82serve to form an undulating form in the lead 60 as is depicted in FIGS.15 a-15 c.

As depicted, the undulating form is substantially sinusoidal with thepeak to peak amplitude of the undulating form substantially constantalong its length. If desired, at least the undulating portion of thelead can be encapsulated within a silicone and/or parylene tube or outerlayer 61, as is depicted in FIG. 15 b.

FIGS. 16 a and 16 b depict an embodiment wherein a stack of a pluralityof sets of wires 14 have passed through the wheels 81,82 to form anundulating lead 70 according to the present invention. In thisembodiment, the lead comprises three sets (71,72,73) of wires 42 stackedone on the other. The undulating portion of the lead has then beenencapsulated in an outer tube 74. Substantially flat-form cables andcables of rectangular or other cross-sections can also be envisaged.

The presence of the undulating form in the lead 70 improves theflexibility of the lead 70 and allows it to compensate for any movementbetween the stimulator and the electrodes 12 of the array. This servesto minimise force on feedthroughs used to connect the wires 14 to thestimulator.

The present invention therefore maintains the layered nature of theconducting element and provides a conducting lead that ensures easyidentification of the conducting portions and their associatedstimulating pads. The present invention also provides for a flexible andcoiled lead that aligns each of the layers of the conductor at eitherend of the lead.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive.

1. An electrically conducting lead comprising: an electrically-insulative elongate body; and an electrically conductive element, wound in an anticlockwise direction for a first length of said body and in a clockwise direction for a second length of said body, having first and second ends and comprising a plurality of layers, each said layer comprising a plurality of electrical conductors positioned within said conductive element such that a first length of each conductor is wound around said body in an anticlockwise direction and a second length of each conductor is wound around said body in a clockwise direction, wherein first ends of each of said conductors at said first end of said conductive element are correspondingly identifiable at said second end of said conductive element as second ends of each of said conductors, based on the corresponding position within said conductive element of each of said first and second ends of said conductors with respect to the positions of the other conductors.
 2. The electrically conducting lead of claim 1 wherein the wound arrangement of the electrically conductive element is a helically wound arrangement.
 3. The electrically conducting lead of claim 1 wherein said electrically conductive element extends from a first end to a second end of said lead.
 4. The electrically conducting lead of claim 3 wherein the longitudinal extent of each of said plurality of electrical conductors over the length of said lead from said first end to said second end is substantially identical.
 5. The electrically conducting lead of claim 4 wherein the longitudinal extent of each of said plurality of electrical conductors over the length of said lead from said first end to said second end is identical.
 6. The electrically conducting lead of claim 1 wherein the length of said conductive element that is wound in an anticlockwise manner is equal to the length of said conductive element that is wound in a clockwise manner.
 7. The electrically conducting lead of claim 6 wherein at the transition from anticlockwise to clockwise windings, said conductive element is folded back on itself.
 8. The electrically conducting lead of claim 1 wherein each of said plurality of layers of said conductive element is comprised of a plurality of separate electrical conductors, with each of said plurality of layers having the same number of conductors as the other layers in said conductive element.
 9. The electrically conducting lead of claim 1 wherein each of said plurality of layers of said conductive element is comprised of a plurality of separate electrical conductors, with the number of conductors of at least one of the of said plurality of layers varying from the number in one, more or all of the other layers of said conductive element.
 10. The electrically conducting lead of claim 1 wherein the electrical conductors are made of platinum.
 11. An electrically conducting lead comprising: an electrically-insulative elongate body; and an electrically conductive element, wound in an anticlockwise direction for a first length of said body and in a clockwise direction for a second length of said body, having first and second ends and comprising a plurality of layers, each said layer comprising a plurality of electrical conductors positioned within said conductive element such that the plurality of electrical conductors are wound in an anticlockwise direction around said body for a first length, and in a clockwise direction around said body for a second length, wherein said plurality of electrical conductors of at least one of the layers varies in number from the number of said plurality of electrical conductors in at least one of the other of said plurality of layers, and wherein said plurality of electrical conductors are positioned within said conductive element such that first ends of each of said conductors at the at said first end of said conductive element are correspondingly identifiable at said second end of said conductive element as second ends of each of said conductors, based on the corresponding position within said conductive element of each of said first and second ends of said conductors with respect to the positions of the other conductors.
 12. The electrically conducting lead of claim 11 wherein the number of conductors in said one of the layers varies from the number in more than one of the other layers of the element.
 13. An electrically conducting lead comprising: an electrically-insulative elongate body; and an electrically conductive element, helically wound in an anticlockwise direction for a first length of said body and in a clockwise direction for a second length of said body, having first and second ends and comprising a plurality of layers, each said layer comprising a plurality of electrical conductors positioned within said conductive element such that the position of each of said plurality of electrical conductors comprising each layer with respect to said plurality of electrical conductors of neighboring layers remain constant between said first and said second ends of said insulative body, wherein each of said plurality of electrical conductors are positioned such that each conductor is wound in an anticlockwise direction around said body for a first length and in a clockwise direction around said body for a second length, and wherein first ends of each of said conductors at the first said first end of said conductive element are correspondingly identifiable at said second end of said conductive element as second ends of each of said conductors, based on the corresponding position within said conductive element of each of said first and second ends of said with respect to the positions of the other conductors.
 14. The electrically conducting lead of claim 1 wherein with the longitudinal extent of each of said electrical conductors over said portion of the lead are substantially identical when in said wound arrangement. 